In a conventional single-sheet printer, sheets of paper are pulled from a stack and fed into the printer's input port so as to begin the print cycle. Such an operation, commonly known as sheet pick-up, is accomplished by peeling the top sheet from the stack using a motor-driven roller. The roller, which generally includes a frictionally adherent rolling surface, rotates against the upper surface of the top sheet, directing passage of that sheet into the printer.
Due to frictional forces between consecutively stacked sheets, pick-up of the top sheet is often accompanied by unwanted pick-up of a second sheet, an event which may lead to paper jam. This problem is particularly prevalent where the input stack is a stiff stack, such stacks being characterized by high frictional forces between sheets.
In order to avoid pick-up of multiple sheets, some printers have been fitted with a device known as a separator. The separator, which includes a frictionally adherent surface, is mounted to the printer adjacent the roller and biased toward engagement therewith. Sheets pulled from the stack are pinched between the roller and the separator so that the roller exerts a first frictional force against the upper surface of the top sheet and the separator exerts a second opposing frictional force against the bottom surface of the second sheet. The top sheet is thus intended to slide across the second sheet and into the printer.
The above-described arrangement, however, has presented several problems. First, known separators have characteristically engaged all sheets entering the printer, including the top sheet. Intake of the top sheet is thus opposed by the separator. Due to the sliding frictional engagement between the top sheet and the separator, previously developed separators have also been characterized by unacceptably rapid wear with such wear leading to excessive downtime and frequent separator replacement. Additionally, after the picked-up sheet passes completely into the printer's input port, and there is no paper separating the roller and the separator, known printers have produced an undesirable whine or squeal due to contact between like surfaces.